The present invention relates to a probe for measuring the level of a liquid in a reservoir, comprising a conducting circuit and means for mounting the circuit inside the reservoir and, arranged so that the length of the circuit which is immersed in the liquid varies with the level of the liquid. the conducting circuit comprising at least one track made from a conducting material on face of which is applied to an insulating substrate and the conducting material has a resistivity which depends on the temperature.
This type of probe is already known, and is described in European patent application No. 0140747. In this known probe, the presence of the substrate forms a hindrance. In fact, the principle of a measurement is as follows. An electric current is passed through the conducting track, which heats up. The heating is different for the part of the track immersed in the liquid and for the part of the track not immersed, because of the thermal inertia of the liquid. Measurement of the total resistance, a certain time after the beginning of the current flow, gives an indication of the level of the liquid. In the probe described in the above-mentioned patent application, the time constant with which the track heats up is high, for it depends, in a rigid way, on the substrate on which the track is bonded, which may falsify the measurement if special arrangements are not made.
The present invention aims at overcoming the preceding drawback.